EP1681230B1 - Bicycle crank assembly for harmonizing the pedalling of the cyclist - Google Patents

Abstract

The assembly has a chain gear comprising a toothed plate (1) whose each half has an area (A) in which radius of a pitch line (2) of tooth increases from its minimum to its maximum. Each half of the plate has an area (C) in which the line radius decreases continuously to its minimum value. A crank (7) has a main axis (6) forming a wedging angle adjustable with an axis (3) connecting points (E, E`) of the line.

Description

The present invention relates to a crankset for a bicycle and more particularly to a crankset comprising a shaft, a pair of cranks and at least one chain gear.

The driving mechanism of the bicycle consists of the crankset according to the invention, a chain gear secured to the hub of the rear wheel, and a drive chain stretched between the chain gear of the pedal and the rear gear.

Each crank end remote from the crank shaft, so-called free end, supports a pedal. The pedals are pushed by the cyclist's feet to transmit torque to the rear gear using the drive chain.

Conventionally, the pedals used consist of a pedal body which comprises a generally horizontal plate, mounted free to rotate about a so-called pedal axis. The plate comprises on at least one of its faces interlocking elements able to cooperate with fastening elements integral with the sole of a shoe of the cyclist. These pedals are called automatic.

Experience has shown that in order to make the best use of the muscles of the lower limbs of the cyclist, it is advantageous to have an increase in the radius of pedaling on the downward arc of the movement of each pedal with, on the contrary, a reduction of this radius. on the ascending arc.

In this regard, we know the improved crank pedal off-axis object of the patent French FR 2 623 769 which discloses a cycle crankset according to the preamble of claim 1. This cycle crank comprises a crank for a circular-shaped plate, provided with a pedal offset by an eccentric device, so that when the pedal is horizontal, the foot support plane is shifted forward by an amount equal to or less than the value of the eccentricity. This device makes it possible to increase the pedaling radius on the downward arc of the movement of each pedal and, on the contrary, to reduce the radius on the ascending arc.

Similarly, the depositor has already imagined pedals, described in the international patent application WO 2004/044458 , where the upper face of the plate extends below the pedal axis along a distance a and where the plane of support of the foot on the plate is in front of said axis along a distance b . These notable improvements improve the distribution of the cyclist's muscular work during pedaling, in particular to reduce fatigue with equal power and work developed. Subsequently, the point of support of the foot on the pedal will be called the point defined by the intersection between the axis of support of the foot (which belongs to the sagittal plane of the cyclist passing through the metatarsal of the big toe) and the top from the sole of the shoe.

Compared to conventional pedals, these pedals marketed under the name of "VISTA" by the applicant, have further advantages. First, with conventional pedals, near the top dead center, the distance separating the fulcrum of the foot on the plate and the axis of rotation of the pedal, distance representing the lever arm of the fulcrum, is equal to the length of the crank to which is added half the thickness of the plate and the thickness of the sole of the shoe. On the contrary, near the bottom dead center, this distance is equal to the length of the crank from which half of the thickness of the plate and the thickness of the sole are subtracted. In the case of the "VISTA" pedals, near the top dead center, the lever arm of the fulcrum is reduced by the length corresponding to the sum of half the thickness of the plate and the distance a, while near the bottom dead center, it is extended by this length. In other words, the "VISTA" pedals provide a reduction of the lever arm when it is maximum in the case of conventional pedals, and vice versa. This aspect helps to reduce the variations of the lever during a cycle of pedaling.

However, a pedal with pedals type "VISTA" is not completely satisfactory. Indeed, the depositor first found empirically that the angular velocity of the straight line passing through the axis of the pedal and by the fulcrum of the foot (hereinafter referred to as the straight line D) is a predominant criterion for the fatigue generated by pedaling. As a result of the many tests he has conducted, a constant angular velocity of this line when the pedal is in the upper anterior quadrant guarantees a reduction in cyclist fatigue for a given effort.

More precisely, this empirical aspect is theoretically explained. At every moment, the power to be supplied to the bicycle is equal to the product of its speed advancement by force necessary to overcome the effects of gravity, the mechanical friction internal to the bicycle and aerodynamic friction. In steady state, this power is globally constant and directly delivered by the drive chain being equal to the product of its speed of travel by the sum of the tangential forces applied by the teeth of the engaged plate. It is known that, in his search for efficiency and maximum efficiency, the cyclist must transmit the most constant power possible to harmonize his pedaling, avoiding jerking in the movements of his legs. Often, when the cyclist is tired, it will provide significant effort in the downward arc of the pedal movement, and almost zero efforts to dead points up and down and in the ascending arc. This type of pedaling is less effective and more tiring than a pedaling where the instantaneous power delivered by the cyclist is as uniform as possible throughout a cycle of pedaling.

In particular, the applicant is committed to the fact that the power developed is generally constant when the pedal describes the upper anterior quadrant where it is known that the pedaling is delicate and damages the muscles, tendons and joints of the knee which is then almost fixed, unlike the other three quadrants. Moreover, because of the presence of two cranks in the construction of a pedal, the configuration of said pedal from a kinematic point of view must be equivalent that the pedals are in the top dead center or bottom dead center. The reasoning that will be followed later for any pedal in its movement in the upper and lower quadrants must also apply for the other pedal when it is in the same quadrants. As a result, the applicant has focused on making the power developed globally constant only in the upper anterior quadrant, the lower anterior quadrant allowing only smooth and smooth return to the kinematic configuration. pedal such as when the pedal was in the top dead center.

However, the power developed at each moment by the cyclist is equal to the product of the tangential force that he applies to the pedal at the point of support, by the distance separating this point from the axis of the pedal (distance previously called lever arm), and by the angular velocity of the straight line D. Thus, the suppression of the variations of the angular velocity D consequently makes it possible to attenuate the variations of the force required to be applied at the fulcrum in order to develop a generally uniform power regardless of the angular position of the crank in the upper quadrant. prior. Since the effort is essentially muscular, it is easy to understand the interest of the economy achieved by a better linearization of the pedaling force, contributing to an increased physiological balance of the cyclist and efforts on the chain and the gears before and behind. better distributed.

In the case of a pedal with "VISTA" pedals, although, at a constant crank rotation speed, the base of the foot describes during the pedaling a constant speed circular curve with respect to a linked fixed reference system. in the frame of the bicycle (the pedal body undergoing a regular circular translation), the line D linking this point to the axis of the pedal has a variable angular speed in its rotational movement about the axis of the pedal. Calculations show that for an angular crank speed of 10 degrees per second, the average angular velocity of the straight line D when the pedal is near the top dead center is approximately 8.4 degrees per second, and 10.8 degrees per second near the bottom dead center. When the crank is close to horizontal, the average angular velocity of line D is 8.8 degrees per second. These average speeds are directly related to the value of distances a and b .

We know the pedalboard object of the patent German DE 2.219.530 which discloses a tray of elliptical shape whose diameter variation and the position of the cranks relative to said elliptical shape of the plate, contribute to reduce the pedaling effort that must provide the cyclist when the crank is in the top dead center.

The present invention aims to combine the technology of the "VISTA" pedals described above with that of a variable diameter plate but of particular non elliptical shape, the combination of these two technologies producing a remarkable and unexpected technical effect which, not only allows the cyclist to pedal by providing a uniform and constant power, but also advantageously allows to obtain a circular movement of the fulcrum of the foot at a non-constant speed ensuring a smooth and non-tiring pedaling for the cyclist and an angular velocity of the line D relative to the axis of the pedal which is substantially constant when the pedal is in the upper front quadrant.

For this purpose and in accordance with the invention, there is provided a cycle crank comprising a shaft, a pair of crank and at least one chain gear adapted to cooperate with a drive chain, each crank supporting at its free end a pedal comprising a pedal body consisting of a plate provided on its upper face with front and rear locking means of a boot and on one of its longitudinal edges of a case containing a pedal axis, free to rotate , able to be fixed to the free end of a crank, the plate being secured to the case so that on the one hand, its upper face extends under the pedal axis along a distance a and that d on the other hand the axis of support of the foot on the plate belonging to the frontal plane of the cyclist passing through the metatarsal of his big toe when pedaling is in front of the pedal axis following a distance b . This pedal is remarkable in that the chain gear consists of at least one variable diameter toothed platform having a central symmetry unique to the axis of crankset, each half of the plate having at least a first zone where the pitch line of the toothing continuously increases from its minimum radius to its maximum radius, and a second zone where the radius of the pitch line continuously decreases to its value minimum, the main axis of the crank adjacent to the plate forming a so-called angle calibration, adjustable with the axis connecting the points of the primitive line for which the radius is minimum.

• la figure 1 représente une schématisation des trajectoires de l'axe de pédale et du point d'appui du pied sur la pédale lors de l'utilisation d'un pédalier comportant des pédales du type « VISTA »,
• la figure 2 représente un exemple de plateau appartenant au pédalier conforme à l'invention, le point de tangence du brin tendu de la chaîne d'entraînement correspondant au rayon minimum de la ligne primitive de la denture du plateau,
• la figure 3 représente une vue en perspective d'un exemple de pédale appartenant au pédalier conforme à l'invention,
• la figure 4 représente un pédalier conforme à l'invention, comprenant deux plateaux.

In the accompanying drawings given by way of non-limiting example of one of the embodiments of the subject of the invention:

• FIG. 1 represents a schematization of the trajectories of the pedal axle and of the point of support of the foot on the pedal when using a pedals having pedals of the "VISTA" type,
• FIG. 2 represents an example of a plate belonging to the crankset according to the invention, the point of tangency of the stretched strand of the drive chain corresponding to the minimum radius of the initial line of the toothing of the plate,
• FIG. 3 represents a perspective view of an example of a pedal belonging to the pedal assembly according to the invention,
• Figure 4 shows a crankset according to the invention, comprising two plates.

Referring to Figure 1, a semicircle C ₁ of center O ₁ (which is the point symbolizing the axis of the pedal) schematizes the trajectory that follows the pedal axis (represented in different positions by the points A ₁ , A ₂ , A ₃ ) when the pedal is in movement, in the upper and lower anterior quadrants. The radius of this half circle C ₁ is equal to the length of the crank, that is to say the distance between the axis of the pedal and the pedal axis. The points B ₁ , B ₂ , B ₃ represent the point of support of the foot on the pedal in different positions of the crank, respectively when the pedal is at the top dead center (axis of the pedal in A ₁ ), horizontally of the axis of the pedals (axis of the pedal in A ₂ ) and in the bottom dead center (axis of the pedal in A ₃ ). Considering that the pedal undergoes a circular translation, at each moment, the point of support of the foot on the pedal is shifted from the pedal axis forward along a distance y and downward along a distance x . The trajectory of the point of support of the foot on the pedal is shown schematically by the semicircle C ₂ identical to C ₁ and centered on the point O ₂ offset from the point O ₁ towards the front of the distance y and towards the top of the distance x. It is understood that the distances x and y are related to distances a and b related to the use of pedals "VISTA": the sum of the distance a and the distance x is equal to the thickness of the sole of the shoe while the distance is equal to the distance b. The straight line through O ₁ and the fulcrum is named D as before and represented through B ₁ . The average angular speed of the crank is called θ ₁ , θ ₂ , θ ₃ near the top dead center, a horizontal position of the crank, and the bottom dead center respectively. The average angular velocity of the line D in rotation relative to O ₁ during pedaling is called w ₁ , w ₂ , w ₃ near the top dead center, a horizontal position of the crank, the bottom dead center.

The calculations show that, when the pedal has a circular plate and pedals "VISTA", and constant crank angular velocity (θ ₁ , θ ₂ , θ ₃ , are equal), the angular velocity of the straight line D increases continuously in the upper and lower anterior quadrants from its minimum value w ₁ reached at the top dead center (in B ₁ ) to its maximum value w ₃ reached at the bottom dead point (in B ₃ ), and decreases continuously in the lower posterior quadrants and higher from B ₃ to B ₁ . Subsequently, the angular speeds previously defined will retain the same references as the pedal is according to the invention or it comprises a circular plate.

Figure 2 shows a chain gear formed by a plateau 1 belonging to a crankset according to the invention, and which allows, remember, to obtain an angular speed of the straight line D generally constant when the pedal describes the upper front quadrant. The primitive line of the teeth of the gear is marked 2. We will call primitive line which corresponds to the pitch radius in the case of a circular plate. In addition, the distance between this point and the bottom bracket axis O ₁ will be referred to as a point in the primitive line. The plate 1 comprises a left part and a right part delimited by the axis 3 (vertical in the figure). The left part of the plate 1 is divided into several zones delimited by angles measured from the axis 3 positively in the opposite direction to the rotation of the plate 1. The direction of rotation of the plate 1 during the driving of the chain 4 is indicated by the arrow f in FIG. 2. The angular values indicated hereafter serve only to illustrate the present example and can thus vary slightly according to, in particular, the construction of the bicycle (dimensions and angles of the frame ) and / or the tastes and anatomy of the cyclist.

The plate 1 comprises a first zone A (0 degree to 60 degrees) where the original line 2 of the toothing passes from its minimum radius to its maximum radius. The point E corresponds to the intersection between the primitive line 2 and the axis 3, and the minimum radius of the primitive line 2 is equal to the distance between the point E and the point O ₁ (pedal axis). The axis 5 passing through the center O ₁ is oriented at an angle of 60 degrees with respect to the axis 3 and the intersection between the axis 5 and the primitive line 2 is marked F. The distance between the points O ₁ and F corresponds to the maximum radius of the primitive line 2. The increase in the radius value of the primitive line 2 is light and continuous. In a particular embodiment, this increase is linear as a function of the value of the angle formed by the straight line passing through the point of the primitive line and the axis of the crankset O ₁ , with respect to the axis 3 passing through. by the points E, E 'of the primitive line 2 minimum radius. The plate 1 has a second zone B (60 degrees at 90 degrees) where the radius of the primitive line 2 remains constant and equal to the maximum radius. Finally, a third zone C (90 degrees at 180 degrees) where the radius of the primitive line 2 returns to its minimum value at a point E ' symmetrical with the point E with respect to O ₁ . It ends the left part of the board 1. The decrease of the radius in this zone is progressive and constant so that the change of radius does not cause jerk in the movement of the pedal and guarantees a harmonious pedaling. In a particular embodiment, this reduction is linear as a function of the value of the angle formed by the straight line passing through the point of the primitive line and the axis of the crankset O ₁ , with respect to the axis 3 passing through. by the points E, E 'of the minimum line 2 of minimum radius. Furthermore, the plate may comprise only the areas A and C which are then adjacent for a value of the angle between 60 and 90 degrees.

Naturally, on the right side of the plate 1, the same zones referenced A ', B' and C 'are arranged so that the plate 1 of a pedal assembly according to the invention comprises two successive similar curves having a single central symmetry by compared to the axis of the crankset O ₁ , and no axial symmetry unlike ellipses.

The pedal is designed so that the radius of the primitive line 2 corresponding to the point of tangency of the stretched strand of the chain 4 is minimum when the pedals are at the top and bottom dead centers. In this configuration, the main axis 6 of the adjacent crank 7 to the plate 1 (Figure 2) coincides with the axis 3, the pedal having a second crank 8 whose main axis is parallel to the main axis 6 of the crank 7. Nevertheless the attachment of the plate 1 to the pedal of the invention is such that it offers the possibility of orienting the main axis 6 of the adjacent crank 7 relative to the axis 3 at an angle φ called calibration between 0 and 20 degrees. This adjustment of the angle φ is obtained by setting means cranks 7, 8 relative to the plate 1, made according to a preferred embodiment by an assembly of the cranks 7,8 on the plate 1, of the interlocking type with teeth or splines which eliminates the degrees of rotation of said cranks 7,8 compared to said plateau 1 according to the axis of rotation of the pedal. These grooves or these teeth make it possible to make a wedging of the axis 6 of the crank 7, and therefore of the crank 8, with respect to the axis 3, said wedging being preferably situated between 0 and 20 degrees. This setting allows the rider to determine, depending in particular on the relative position of the saddle relative to the seat post, the angular position of the crank relative to the vertical axis passing through the top and bottom dead centers of the pedals. when the point of tangency of the stretched strand of the chain 4 enters the zone B. More precisely, if the saddle is behind, the angle φ must be positive in the trigonometrical direction, whereas when it is in front, the angle φ must be negative.

In practice, we will make sure that the minimum radius is smaller and the maximum radius is greater than the original radius of a circular plate of the same development globally. When φ is zero (which represents most cases), when the radius of the primitive line 2 at the point of tangency of the stretched strand of the chain 4 is less than the primitive radius of a circular plate of the same global development, we create artificially an increase in the angular velocity of the adjacent crank 7. The angular velocity of the line D will be increased accordingly with respect to the speed it would have in the case of a circular plate to an angular position of the crank adjacent 7 with respect to a vertical axis such that the radius of the primitive line 2 at the point of tangency of the stretched strand of the chain 4 is equal to the pitch radius of the circular plate of the same overall development. Beyond this angular position of the adjacent crank 7, the rotational speed of the crankset is decreased compared to that it would have in the case of a circular plate of the same overall development, causing a decrease in the angular velocity of the line D until the point of tangency of the stretched strand of the chain 4 enters the zone C of the plateau 1. In other words, the shape of the plate 1 makes it possible to increase the angular velocity of the straight line D in the angular sector of the upper anterior quadrant of the movement of the pedal where this speed would be low in the case of use with a circular plate , and to decrease it in the remaining angular sector of the same quadrant.

The ratio between the maximum and minimum radii of the primitive line 2 is substantially equal (or slightly greater for the small and medium trays: an increase of about 1% is then expected) to the ratio of the angular velocity W ₁ of the straight line D when the pedal is close to the top dead center by the angular velocity w ₂ of the line D when the adjacent crank 7 is close to the horizontal, w ₁ and w ₂ being determined in the case where the drive chain 4 cooperates with a circular plate. Thus, if φ is zero, the ratio between the mean angular velocity θ ₁ of the adjacent crank 7 by its mean angular velocity θ ₂ is equal to the previous ratio of the radii. On the other hand, the average angular velocity of the straight line D is generally constant when the pedal describes the upper anterior quadrant.

Each free end 9 of crank 7, 8 comprises a pedal 10 shown in Figure 3 as described in the international patent application WO 2044/044458 on behalf of the applicant. Briefly, each pedal 10 comprises a pedal body 11 consisting of a horizontal plate 12 provided on one of its longitudinal edges with a case 13 containing the pedal shaft 14 free to rotate, adapted to be fixed to the end 9 of a crank 7, 8. The plate 12 has on its upper face 15 and 15 front locking means of a boot. The plate 12 is secured to the housing 13 so that, on the one hand, its upper face extends below the axis of pedal 14 according to the distance a and second foot support (included in the frontal plane passing through the metatarsal of the big toe of the cyclist when the latter pedal) is in front of the pedal axis 14 along the distance b. According to a particular non-limiting embodiment, the front locking means 15 consists of a pin extending vertically from the upper face of the plate 12 in its front part and comprising a flange 17 serving as a retainer. This stud is able to cooperate with the front part of a wedge secured to the sole of the shoe. The wedge has a V shape at the bottom of which is formed a semicircular recess of diameter just greater than the diameter of the stud. Furthermore, the rear locking element 16 consists of a claw 18 hinged about an axis at the rear of the plate 12, parallel to the axis of the pedal 14. The lower end of this claw 18, cooperates with a return spring to suppress the pivoting caused by the application of a force on the upper end. The reader may refer to the aforementioned international application where this type of pedal marketed by the applicant under the name "VISTA" is described in more detail.

For example, the average angular value w ₁ is determined when the crankset comprises a circular plate from the value range taken by the instantaneous angular speed of the line D when the main axis 6 of the adjacent crank 7 rotates by one. vertical position to a position inclined 30 degrees from the vertical position where the pedal 10 is in the upper anterior quadrant. Likewise, the average angular velocity w ₂ is determined from the value range taken by the instantaneous angular velocity of the straight line D when the main axis 6 of the adjacent crank 7 rotates from a position inclined by 70 degrees relative to vertically to a position where it is horizontal. In practice, this ratio is roughly equal to 1.04, but it should be noted that it depends on the value of distances a , b .

According to another object of the invention, the crankset consists of two plates 19, 20 as shown in FIG. 4. The two plates 19, 20 have an identical design, in accordance with the technical characteristics described above, namely a first zone A where the primitive line increases continuously from its minimum radius to its maximum radius, possibly a second zone B where the primitive line remains constant and equal to the maximum radius, then a third zone C where the primitive line continuously decreases from its maximum radius to at its minimum radius, with the possibility to direct the cranks 7,8 following a tab φ of wedging compared to trays 19,20. They have different diameters, one 19 constituting the large plate of the pedal and the other 20 the small plate.

According to a remarkable mode of design, the plates 19, 20 have a wedge angle δ between the axis 21, passing through the point O ₁ and the maximum radius of the primitive line of the large plate 19, and the axis 22, passing through the point O ₁ and the maximum radius of the primitive line of the small plateau 20.

The wedging angle δ between the two plates 19, 20 is adjustable and advantageously makes it possible to optimize the pedaling conditions of the user, depending on whether the chain 4 is positioned on the large plate 19 or on the small plate 20. indeed, depending on the conditions of use, the point of tangency of the chain 4 varies due to the difference in diameter between said plates 19,20, which affects the position of the user. Thus, the user will have the bust leaning forward when the chain 4 meshes with the large plate 19 and bust straightened when the chain 4 meshes with the small plate 20. This position of the bust considerably changes the position of the pegs relative to the legs ; hence the importance of being able to modify the angle of wedge δ between the two plates 19,20 to obtain a position of the point of tangency offering the optimal conditions of pedaling specific to each user.

According to a preferred embodiment, not shown in the figures, the wedging means between the two plates 19, 20 are constituted by an assembly of the interlocking type with teeth or splines which makes it possible to rotate the two plates 19,20, with the possibility of modifying the stall angle δ to optimize the pedaling conditions of the user.

Finally, the reader will understand that the pedal according to the invention must simultaneously include pedals of the "VISTA" type and at least one plate as previously described because, in the event that the pedal is equipped with conventional pedals, calculations show that the ratio between the minimum radius and the maximum radius of the primitive line 2 would be 1.25. The torque delivered by the plate 1 directly dependent on the value of the radius of the primitive line 2 would vary according to the same ratio. Moreover, still in this hypothesis, although the angular velocity of the line D is generally constant, the speed of the point of support of the foot on the pedal plate would vary in the same ratio: the ratio of the speed of this point the top dead center speed when the crank is horizontal would be 1.25, pedaling then not harmonious and particularly tiring from a muscular point of view.

Finally, it goes without saying that the examples that have just been given are only particular illustrations in no way limiting as to the achievements of the crankset according to the invention according to the following claims.

Claims (11)

1. Cycle crank gear comprising a shaft, a crank pair (7, 8) and at least one chain gear suitable for engaging with a driving gear (4), each crank (7, 8) supporting at the free end (9) thereof a pedal (10) comprising a pedal body (11) consisting of a plate (12) provided on the top face thereof with front (15) and rear (16) shoe locking means and on one of the longitudinal edges thereof with a casing (13) containing a so-called pedal shaft (14), free in rotation, suitable for being secured on the free end (9) of a crank (7, 8), the plate (12) being rigidly connected to the casing (13) such that, firstly, the top face thereof extends under the pedal shaft (14) along a distance a and, secondly, the shaft supporting the foot on the plate (12) belonging to the cyclist's front plane passing through the metatarsal of the big toe of same while pedalling is located in front of the pedal shaft (14) along a distance b characterised in that the chain gear consists of at least one variable diameter geared plate (1) having a single central symmetry with respect to the crank gear shaft (O₁), each half of the plate (1) having at least a first zone (A) where the pitch line (2) of the toothing increases continuously from the minimum radius thereof to the maximum radius thereof, and a second zone (C) where the radius of the pitch line (2) decreases continuously to the minimum value thereof, and a second zone (C) where the radius of the pitch line (2) decreases continuously to the minimum value thereof, the main shaft (6) of the adjacent crank (7) to the plate (1) forming a so-called adjustable blocking angle ϕ with the shaft (3) connecting the points (E, E') of the pitch line (2) for which the radius is minimum.
2. Cycle crank gear according to the above claim characterised in that the ratio of the maximum radius of the pitch line (2) with respect the minimum radius is overall equal or slightly greater than the ratio of the mean angular speed (w₁) of the line D joining the crank gear shaft (O₁) to the support point (B₁, B₂, B₃) of the cyclist's foot on the pedal (10) when it is located in the vicinity of the top dead centre with respect to the mean angular speed (w₂) of said line D when the crank (7, 8) supporting said pedal (10) is in the vicinity of a horizontal position, the mean angular speeds (w₁, w₂) being determined if the driving chain (4) engages with a circular plate.
3. Cycle crank gear according to the above claim characterised in that the plate (1) comprises a zone (B) inserted between the zones (A), (C), for which the radius of the pitch line (1) is constant and equal to the maximum radius.
4. Cycle crank gear according to any of the above claims characterised in that the blocking angle ϕ is between 0 and 20 degrees.
5. Cycle crank gear according to any of claims 3 or 4 characterised in that the zone (A) extends in the angular sector between 0 and 60 degrees, the zone (B) in the angular sector between 60 and 90 degrees, and the zone (C) in the angular sector between approximately 90 and 180 degrees, the previous angles being firstly measured from the shaft (3) joining the points (E, E') of the pitch line (2) for which the radius is minimum, and, secondly, measured positively in the direction opposite the rotation of the plate (1) during the drive of the chain (4).
6. Cycle crank gear according to any of the above claims characterised in that the value of the radius at a point of the pitch line (2) of the zone (A) of the plate (1) increases linearly as a function of the value of the angle formed by the line passing via said point and by the crank gear shaft (O₁), with respect to the shaft (3) passing through the points (E, E') of the pitch line (2) having a minimum radius.
7. Cycle crank gear according to any of the above claims characterised in that the value of the radius at one point of the pitch line (2) of the zone (C) of the plate (1) decreases linearly as a function of the value of the angle formed by the line passing through said point and by the crank gear shaft (O₁), with respect to the shaft (3) passing through the points (E, E') of the pitch line (2) having a minimum radius.
8. Cycle crank gear according to any of claims 2 to 7 characterised in that the mean angular speed (w₁) is determined on the basis of the value range adopted by the instantaneous angular speed of the line (D) when the main shaft (6) of the crank (7, 8) supporting the pedal (10) rotates by a vertical position to a position inclined by 30 degrees with respect to the vertical, where the pedal (10) is located in the upper front quadrant of the trajectory thereof during a pedalling cycle.
9. Cycle crank gear according to any of claims 2 to 8 characterised in that the mean angular speed (w₂) is determined on the basis of the value range adopted by the instantaneous angular speed of the line (D) when the main shaft (6) of the crank (7, 8) supporting the pedal (10) rotates from a position inclined by 70 degrees with respect to the vertical, where the pedal (10) is located in the upper front quadrant of the trajectory thereof during a pedalling cycle, to a position where said crank (7, 8) is horizontal.
10. Cycle crank gear according to any of the above claims, characterised in that it comprises two variable diameter geared plates (19, 20), having an adjustable blocking angle δ between said plates (19, 20).
11. Cycle crank gear according to any of the above claims characterised in that the front locking means (15) consists of a stud extending vertically from the top face of the plate (12) in the front part thereof, comprising a retaining ring (17), said stud being suitable for engaging with a complementary shape produced in the front part of a block rigidly connected to the sole of the cyclist's shoe, and in that the rear locking means (16) consists of a claw (18) pivoting about a shaft parallel with the pedal shaft (14), rotation being obtained by the application of an effort by the cyclist on the top end thereof, and wherein the lower end engages with a return spring.

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